If the devices agree on odd parity as an error-checking system, the sending device adds an extra bit set to either 0 or 1 to make the total number of bits add up to an odd number. For example, the 7-bit ASCII code for the letter A is 1000001, which adds up to 2, an even number. The sending device would add an extra 1 to make it odd. The receiving device adds up the bits. If the total is odd, chances are the message is OK; if it's even, there was an error in the transmission.

If the devices agree on even parity, the sending device adds an extra bit set to either 0 or 1 to make the total number of bits an even number.

DCD, DSR/DTR and XON/XOFF are different protocols that a peripheral device can use to tell the computer things like "I'm ready when you're ready" or "Give me a second to catch my breath." Signals that regulate the flow of data between the computer and a peripheral device are called handshake signals.

Don't change these settings unless the manual that came with your device specifically tells you to set them in a particular way.

DCD stands for Data Carrier Detect; DSR for Data Set Ready; and DTR for Data Terminal Ready. XON and XOFF are ASCII characters. XOFF tells the transmitting device to halt transmission of characters. XON tells the transmitting device to resume transmission of characters.

If you have a memory expansion card connected to your Apple IIGS, you can designate a portion of the memory on the card to be used as a RAM disk. A RAM disk is memory that is treated like a disk. You format it, access it by volume name, and copy or save applications and documents on it. The advantage of using a RAM disk is that the computer can get information from it much faster than from a disk. The disadvantage is that anything stored on the RAM disk is lost when you turn off the power.

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Appendix A: The Control Panel Program